Jet engine operation



efficiency and apparatus therefor. .relates to a method for improving combustion stability "improving the operation of JET ENGINE OPERATION Robert M. 'Schirmer, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Sept. '12, 1955, Ser. No. 533,785 1 Claim. (Cl. 60--39.06)

This invention relates to jet engines. In one aspect it relates to a method for increasing jet engine operating In another aspect it and combustion efficiency in jet engines employing a single fuel in which a vaporized portion of the fuel is burned in a pilot area to stabilize continuous combustion of the liquid portion of the fuel. p A serious problem-in jet propulsion engines is the occurrence of unstable combustion as the operating conditions of the engine become more severe. With the onset of combustion instability, the flame in the combustion chamber is partially extinguished or fluctuates back and forth; Combustion instability'can progress to the extent that the flame blows out; i.e., the fire is extinguished. Inturbojet engines rich-mixture blow-out is a controlling characteristic of engine performance because it can define the maximum thrust output at a given altitude. In' the combustion chamber of a gas turbine power plant, it is necessary to achieve stable and efiicient combustion of fuel and air' at extremely high rates of heat release in a'relatively confined space through which a stream of air is moved at high velocity.

, Prior art has suggested numerous solutions to the combustion problem in jet engines. One suggestion has been to reduce-air velocity in the flame piloting region in the burner in order to stabilize combustion.

One disadvantage in attempting to stabilize combus- This laydown of carbon also Another prior art method of operation involves the use of liquefied normally gaseous fuels in jet engines but .the difficulties attendant thereto are serious because of the need for pressure tanks and because of the low density of the liquid fuel. Safety hazard of high vapor pressure fuel is also a disadvantage.

An object of my invention is to provide .a method for jet engines using normally liquid jet engine fuels. x

Another object of my invention is to provide a. method' for improving the operation of jet engines using nor- .mally liquid jet engine fuels without cracking of the fuel to produce combustion stabilizing fuel gases.

Another object of my invention is to provide a method .for improving jet engine operation-requiring the use of 5 only one liquid fuel.

Another object of my invention is to provide apparatus and a method for increasing jet engine efiiciency and altitude operational limits.

Still another object of my invention is to provide a method for improving jet engine rich mixture operation.

Yet. another object of my invention'is to provide apparatus for carrying out the method of my invention.

The above mentioned objects and other objects and Patented vOct. 11, 1960 ICC- 2 advantages of my invention will be realized upon reading the following description and attached drawing which respectively describes and illustrates preferred embodiments of my invention.

My invention is particularly directed to an improved method of operating jet propulsion engines whereby the combustion stability, that is, the maximum stable combustor temperature rise is increased by evaporating, without cracking, a portion of the fuel and burning this vaporous fuel to stabilize the combustion of the liquid portion of the fuel. I prefer to evaporate said portion of the fuel in a coil positioned in the combustor or'combustion chamber or in the turbine exhaust, passing the heated fuel to a liquid-vapor separator, removing the liquid portion recovered in the separator and burning it in the main combustion air stream as the primary fuel and burning the vaporized portion of the fuel recovered in the separator in a piloting area of the combustor.

One important advantage of my invention resides in the use of a single fuel and vaporizing a portion of this fuel, without cracking, burning the vapors in a piloting area of the combustion zone and utilizing the resulting ,flame to stabilize combustion of the liquid fuel by which .operation combustion stability is improved. This method 25.

of operation is particularly effective in improving the combustion stability and the combustion efiiciency in continuous combustion systems operating at high rates of heat release. The method of operating a jet engine disclosed herein is applicable to continuous combustion processes in general, such processes being used in, for example, stationary gas turbine po-wer plant as Well as aircraft jet engines, such as turbojet, turboprop and similar types of continuous combustion engines.

In one embodiment, the invention comprises heating the liquid fuel in a closed coil in the combustion chamber, Without crackingflby indirect heat exchange with the combustion gases produced in the combustor, passing the thus' heated fuel to a liquid-vapor separator, passing the vaporized fuel from the separator to the piloting area of I the combustor and injecting the remaining and liquid por- .tion of the fuel into the main combustion air stream. An

alternative of this mode of operation involves dividing a stream of liquid fuel from the storage tank into two portions, injecting one portion directly into the main combustion air stream and vaporizing at least some of the other portion without cracking in indirect heat exchange with the combustion gases produced in the combustor and passing thevaporized portion of the fuel to a pilot 'burner for stabilizing the combustion of the liquid fuel inthe combustor.

Unless a major part of the indirect heat exchanged portlon is vaporized, it usuallyis preferable to provide a separator for separating the vapors from the unvaporized portion, the latter being combined with the main stream of liquid fuel passing to the main combustion air stream. I have found that an increase in combustion stability, that is, a maximum stable combus- 'tor temperature rise can be obtained from either of the .previously mentioned modes of operation. Since the flame piloting area is the most critical area for flame stabilization, my process which involves vaporization of only a relatively small portion of the fuel is a marked improvement over any of the methods which involve vaporization of most or all of the "fuel and which, therefore, result in considerably greater amounts of carbon and gum deposited in the vaporizer tubes.

If only a portion of the liquid fuel is passed through the heat exchange coils, a larger proportion of this heated liquid will have to be vaporized to i provide suflicient vapors for combustion stabilization than when the en- ;tire volume of liquid fuelis passed through the coils. The coils are so designed as'to give as muchvaporizaplurality tion aspossible at high'fuel flow rates while not permitting cracking at lower fuel flow rates.

If it is desired to vaporize all the fuel in the above mentioned .alternative mode of operation, a lighter and more easily vaporized fuel or one-at least "freefrom heavy, high boiling ends should be used.

In the drawing, Figure 1 illustrates, in diagrammatic form, a longitudinal view, partly in section, of a preferred embodiment of apparatus of my invention.

FigureZ is an elevational view, partly in section, of another embodiment of my invention.

Figure 2a illustrates a modification of a portion of the apparatus of Figure 2.

Referring now to the drawing and specifically to Figure 1, reference numeral 11 identifies a combustion zone or combustor which is substantially an elongated open end vessel of circular cross-section. Within this vessel 11 is a basket type flame tube 12, in the inlet end of which is positioned agas pilot nozzle 23. Downstream as regards direction of combustion gas flow is a liquid atomizing nozzle 24. In the walls of basket type flame tube 12 is a plurality of openings 14 for inlet of primary combustion air. Further downstream is a plurality of secondary air inlets 13 for admission of quench air to the hot combustion gases. .Still further downstream and at a point near the outlet end of the combustor 11 is a closed coil 16. A liquid fuel storage tank 15 to which is connected a pipe 26 provided with a pump 25 for passage of liquid fuel to the heating coil 15 is provided. From coil 16 heated fuel flows through a conduit 19 to a phase separator tank 20. Pipe 21 leads from the top of the separator to the gas pilot nozzle 23. Pipe 22 provided with a pump 22a conducts liquid fuel from the separator tank to the liquid atomizing nozzle 24. Reference numerals 17 and 18 identify, respectively, the combustion gas outlet and the air inlet for the combustor 11.

For starting up operations, if desired, a by-pass pipe 19a, with valve 1%, is provided as shown in Figure 1, a valve 190 being provided also in pipe 19 between bypas pipe 19a and the phase separator 20. By use of this by-pass pipe the phase separator 20 does not become .filled with liquid fuel.

In the operation of the apparatus of Figure 1, liquid fuel, such as gas oil, kerosene, conventional jet fuels, .nheptane, isooctane, and the like, passes from storage tank 15 by pump 25 through pipe 26 to heating coil 16 in which the required amount of heating takes place. Itis essential to the operation of my process that the heating in coil 16 be so controlled as to avoid any cracking of the fuel being heated. The thus heated fuel passes on through pipe 19 into separator tank 20. The main portion of the fuelseparated in tank 20 is in the liquid phase and this fuel is injected through the atomizing nozzle.24 in an upstream direction in the combustion chamber. .Vaporous fuel from separator 20 is injected into the combustion chamber in the pilot flame area through .the gas pilot nozzle.23 The burning of this. gaseous fuel with a relatively small volume of air introduced through the restricted opening 27 results in the production of a very stable flame which pilots the .combustion of the atomized liquid fuel from the atomizing nozzle 24. The openings 14 for air inlet are of a suflicient number and size to provide the required amount of air for burning of the atomized fuel. The quench air openings 13 are of suflicient number and size to admit quench air for cooling the combustion gases so as not to overheat the heat exchange coil 16'and the gas turbine which is positioned downstream of outlet.17.

The combustor assembly illustrated in Figure 1 is .usually one of a plurality of such combustors positioned around a circle in a jet engine, in which case a single phase. separator (20) manifolded to the individual combustors, is preferred. As in conventional jet engine construction, the of combustors discharge their combustion gases to the jet engines turbine for operating a compressor which in :turnsupplies airfor supporting combustion of .Figure 1, the liquid to be depend on the amount the pilot fuel and of the main atomized liquid fuel. In the embodiment of Figure 1, under conditions when a plurality of combustors, one of which is illustrated in this figure, are disposed around a turbine shaft, a coil and liquid-gas separator could be provided for each unit. An alternative is to provide the required number of coils (possibly one for each unit) and manifold the coils to a single separator, and then manifold the separator to each gas and each liquid nozzle. Another alternative is to position one vaporizing coil in the turbine exhaust. and to manifold the separator to each gas and each liquid nozzle. When using a vaporizing coil in a combustor, it is preferable to provide more than one combustor with a vaporizing coil so heating of the fuel can be sufficiently mild as to avoid cracking with the simultaneous laydown of solid carbonaceous matter.

The particular design as regards inside diameter of the pipe of heat exchanger 16, its thickness andlength will need to be so chosen as. to heat to a desired extent, i.e., without cracking, the entire volume of liquidifuel. The heat exchanger should be designed to give the desired amount of vaporization, without cracking, at maximum fuel flow rate, due allowance being given to the prevention of cracking at the longer residence times associated with lower flow rates. This design will be dependent upon the type of fuel .used, the relative volume'ofgaseous fuel required for combustion stabilization, and on other variables as, for example, the type of jet engine, that is, an aircraft engine or a stationary engine and upon many other variables which will be understood by those skilled in the jet engine art.

Figure 2 illustrates a second embodiment of combustor in which only a portion of the liquid fuel is passed through the heat exchanger for partial or substantially complete vaporization. For complete vaporization of the portion of the fuel which passes through, for example, coil 46, an easily vaporized fuel, that is one free from high boiling materials or heavy ends is necessary. Under the condition when'only a portion of the fuel passing through coil 46 of Figure 2 is vaporized, it may be desirable to provide a phase separator 57 (Figure 2a) to separate the vapor and liquid. A separate pipe 64 is then provided'for adding this separated liquid to that in pipe 50. However, since the liquid from coil 46 is hot, it is usually desirable to pass it along with the vapor to the pilot nozzle 51.

In this embodiment (Figure 2) a combustor 41 houses a flame tube 42. Reference numerals 43 and 44 identify, respectively, the outlet end as regards combustion gas outflow from the flame tube and the air inlet end thereof. Positioned axially and largely within flame tube 42 is the pilot flame tube 54 into which pilot nozzle 51 discharges gaseous fuel. A restricted opening 55 at the upstream end of pilot flame tube 54 allows admission'of a restricted flow of air so that the gaseous fuel will burn as a stable flame to pilot combustion of the liquid fuel atomized into the flame tube 42 through atomizing nozzles 52. Asole liquid fuel is stored in tank 45 and this fuel passes through a pipe 56 under the influence of a pump 53 into a vaporizing coil 46. From this coil fuel passes on through a pipe 49 .into the gas nozzle 51. Liquid fuel is bypassed from vaporization coil 46 through a pipe 50 for injection directly into the atomizing nozzles 52. The operation of the embodiment illustrated in Figure 2 is in principle the same as the embodiment illustrated in difference being that only that portion of the vaporized is passed through the heating coil 46 in place of heating the entire volume of liquid fuel. Whether a liquid-gas separator is needed in line-49'Wil1 of heavy ends in the fuel.

The outlets 17 of combustors 11 of Figure 1 usually discharge combustion gases into a turbine nozzle box, not shown, from which they pass through the turbine.

The apparatus illustrated in Figure 2, like that 'of Figure 1, is usually merely one of a plurality of combustors for positioning around the.turbine shaft in a jet engine.

The outlets 47 of combus-tors 41 usually discharge combustion gases into a turbine nozzle box, not shown, from which these gases pass through the turbine. The particular arrangement of comb ustors illustrated in Figures 1 and 2 in a jet engine forms no part of my invention. When a plurality of combusto-rs is positioned in a jet engine, it is intended that one or more combustors be provided with a liquid fuel heating coil 16 or a liquid fuel vaporizing coil 46 as desired for producing vaporous fuel for stabilization of flame within each respective combustor.

The fuel which is used in such a jet engine as herein described, includes conventional jet engine fuels, such as gas oils, kerosene, aviation gasoline, and other hydrocarbon fuels. Heating coils 16 and 46 are preferably made of stainless steel, such as 18-8 or 25-25 steels, or other materials which can withstand the elevated temperatures sufficiently well to offer a reasonable length of useful life. The liquid hydrocarbon fuel is heated in the coils to a temperature above about 200 F. but below the cracking temperature of the particular hydrocarbon fuel employed. The amount of fuel vaporized in the coils will depend to some extent upon the operation of the engine. For example, under full load or high power conditions the residence time of the fuel in the coils will be relatively short, and consequently the fuel will not be heated to as high a temperature as under idling or cruising conditions in which the fuel will have a longer residence time in the coils. In the embodiment of Figure 2, substantially a constant volume of vaporized fuel is supplied to the pilot area irrespective of the engine operating conditions when a metering pump 53a is inserted in line 56.

Proportioning apparatus such as required downstream of pump '53 of Figure 2 to divide the portion to pass to the vaporizing coil 46 from that passing through pipe 50 is illustrated as metering pump 53a, and other auxiliary apparatus is not shown in the drawing nor described in the specification for purposes of brevity and simplicity. However, the need for, and the installation of such apparatus parts, are understood by those skilled in the art.

While certain embodiments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto.

I claim:

In a method for operating a combustion zone with a single liquid fuel, the improvement comprising vaporizing a portion of said liquid fuel by heating the liquid fuel to a temperature at which said portion vaporizes without cracking, separating the vaporized portion from the unvaporized liquid portion of said fuel, atomizing the unvaporized liquid portion of said fuel into a combustion zone having aninlet and an outlet as regards direction of flow of gases therein, burning the atomized portion of said fuel in said zone and directing the flame thereof toward said inlet of said zone, burning the vaporized portion of said liquid fuel intermediate the point of atomizing of said unvaporized liquid portion of said fuel and said inlet of said zone, and directing the flame of the burning vaporized portion of said liquid fuel into the flame of the burning unvaporized portion of said liquid fuel thereby maintaining continuous and uninterrupted combustion of the burning atomized portion of said fuel.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,355 Whittle July 16, 1946 2,542,953 Williams Feb. 20, 1951 2,621,477 Powter et al Dec. 16, 1952 2,635,426 Meschino Apr. 21, 1953 2,664,703 Whitelaw Jan. 5, 1954 2,679,137 Probert May 25, 1954 2,694,899 Hague Nov. 23, 1954 2,720,753 Sharpe Oct. 18, 1955 FOREIGN PATENTS 701,320 Great Britain Dec. 23, 1953 715,197 Great Britain Sept. 8, 1954 

